curl --request POST \
  --url https://whitebit.com/api/v4/main-account/smart-flex/investments/invest \
  --header 'Content-Type: application/json' \
  --header 'X-TXC-APIKEY: <api-key>' \
  --header 'X-TXC-PAYLOAD: <api-key>' \
  --header 'X-TXC-SIGNATURE: <api-key>' \
  --data '
{
  "plan": "8f2e9d3c-1a4b-4c2d-9e5f-6a7b8c9d0e1f",
  "amount": "1000.500000",
  "withReinvest": true,
  "request": "{{request}}",
  "nonce": 1594297865000
}
'

import requests

url = "https://whitebit.com/api/v4/main-account/smart-flex/investments/invest"

payload = {
    "plan": "8f2e9d3c-1a4b-4c2d-9e5f-6a7b8c9d0e1f",
    "amount": "1000.500000",
    "withReinvest": True,
    "request": "{{request}}",
    "nonce": 1594297865000
}
headers = {
    "X-TXC-APIKEY": "<api-key>",
    "X-TXC-PAYLOAD": "<api-key>",
    "X-TXC-SIGNATURE": "<api-key>",
    "Content-Type": "application/json"
}

response = requests.post(url, json=payload, headers=headers)

print(response.text)

const options = {
  method: 'POST',
  headers: {
    'X-TXC-APIKEY': '<api-key>',
    'X-TXC-PAYLOAD': '<api-key>',
    'X-TXC-SIGNATURE': '<api-key>',
    'Content-Type': 'application/json'
  },
  body: JSON.stringify({
    plan: '8f2e9d3c-1a4b-4c2d-9e5f-6a7b8c9d0e1f',
    amount: '1000.500000',
    withReinvest: true,
    request: '{{request}}',
    nonce: 1594297865000
  })
};

fetch('https://whitebit.com/api/v4/main-account/smart-flex/investments/invest', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

<?php

$curl = curl_init();

curl_setopt_array($curl, [
  CURLOPT_URL => "https://whitebit.com/api/v4/main-account/smart-flex/investments/invest",
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_ENCODING => "",
  CURLOPT_MAXREDIRS => 10,
  CURLOPT_TIMEOUT => 30,
  CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
  CURLOPT_CUSTOMREQUEST => "POST",
  CURLOPT_POSTFIELDS => json_encode([
    'plan' => '8f2e9d3c-1a4b-4c2d-9e5f-6a7b8c9d0e1f',
    'amount' => '1000.500000',
    'withReinvest' => true,
    'request' => '{{request}}',
    'nonce' => 1594297865000
  ]),
  CURLOPT_HTTPHEADER => [
    "Content-Type: application/json",
    "X-TXC-APIKEY: <api-key>",
    "X-TXC-PAYLOAD: <api-key>",
    "X-TXC-SIGNATURE: <api-key>"
  ],
]);

$response = curl_exec($curl);
$err = curl_error($curl);

curl_close($curl);

if ($err) {
  echo "cURL Error #:" . $err;
} else {
  echo $response;
}

package main

import (
	"fmt"
	"strings"
	"net/http"
	"io"
)

func main() {

	url := "https://whitebit.com/api/v4/main-account/smart-flex/investments/invest"

	payload := strings.NewReader("{\n  \"plan\": \"8f2e9d3c-1a4b-4c2d-9e5f-6a7b8c9d0e1f\",\n  \"amount\": \"1000.500000\",\n  \"withReinvest\": true,\n  \"request\": \"{{request}}\",\n  \"nonce\": 1594297865000\n}")

	req, _ := http.NewRequest("POST", url, payload)

	req.Header.Add("X-TXC-APIKEY", "<api-key>")
	req.Header.Add("X-TXC-PAYLOAD", "<api-key>")
	req.Header.Add("X-TXC-SIGNATURE", "<api-key>")
	req.Header.Add("Content-Type", "application/json")

	res, _ := http.DefaultClient.Do(req)

	defer res.Body.Close()
	body, _ := io.ReadAll(res.Body)

	fmt.Println(string(body))

}

HttpResponse<String> response = Unirest.post("https://whitebit.com/api/v4/main-account/smart-flex/investments/invest")
  .header("X-TXC-APIKEY", "<api-key>")
  .header("X-TXC-PAYLOAD", "<api-key>")
  .header("X-TXC-SIGNATURE", "<api-key>")
  .header("Content-Type", "application/json")
  .body("{\n  \"plan\": \"8f2e9d3c-1a4b-4c2d-9e5f-6a7b8c9d0e1f\",\n  \"amount\": \"1000.500000\",\n  \"withReinvest\": true,\n  \"request\": \"{{request}}\",\n  \"nonce\": 1594297865000\n}")
  .asString();

require 'uri'
require 'net/http'

url = URI("https://whitebit.com/api/v4/main-account/smart-flex/investments/invest")

http = Net::HTTP.new(url.host, url.port)
http.use_ssl = true

request = Net::HTTP::Post.new(url)
request["X-TXC-APIKEY"] = '<api-key>'
request["X-TXC-PAYLOAD"] = '<api-key>'
request["X-TXC-SIGNATURE"] = '<api-key>'
request["Content-Type"] = 'application/json'
request.body = "{\n  \"plan\": \"8f2e9d3c-1a4b-4c2d-9e5f-6a7b8c9d0e1f\",\n  \"amount\": \"1000.500000\",\n  \"withReinvest\": true,\n  \"request\": \"{{request}}\",\n  \"nonce\": 1594297865000\n}"

response = http.request(request)
puts response.read_body